(a) Technical Field
The present invention relates to an exhaust system of a fuel cell system, and more particularly, to a device for decreasing the concentration of hydrogen discharged to the atmosphere together with air from the fuel cell system.
(b) Description of the Related Art
In general, a fuel cell system generates electrical energy by supplying air and hydrogen to a fuel cell and uses an electrochemical reaction of the hydrogen and oxygen generated by the fuel cell. For example, fuel cell systems are used for operating driving sources such as an electric motor in vehicles, ships, trains, and airplanes.
Fuel cell systems include a stack of fuel cells, a hydrogen supplier that supplies hydrogen to the anodes of the fuel cells, an air supplier that supplies air to the cathodes of the fuel cells, and a heat/water control unit that removes heat and water, which are reaction by-products from the fuel cells, and controls the operational temperature of the stack.
In a polymer electrolyte membrane fuel cell, an appropriate amount of water is required for smooth operation of an ion exchange membrane of a membrane-electrode assembly (MEA), so fuel cell systems have a humidifier that humidifies a reaction gas that is supplied to the stack.
Such a humidifier humidifies air supplied from an air supplier, using water in high-temperature and high-humidity air discharged from the cathodes of fuel cells, and supplies the humidified air to the cathodes of the fuel cells.
Further, fuel cell systems include a hydrogen recycler that mixes the hydrogen discharged from the anodes of fuel cells with the hydrogen supplied from a hydrogen supplier, and supply the mixture back to the anodes.
While a fuel cell system is operated, impurities such as nitrogen and vapor are accumulated in the anodes of fuel cells, so the concentration of hydrogen decreases, and when the concentration of the hydrogen excessively decreases, cell separation may occur in the fuel cell stack.
In order to solve these problems, when a fuel cell system is started and operated, a purge valve periodically opened and impurities are discharged with hydrogen from the anodes, thereby maintaining the concentration of hydrogen at the anodes at a predetermined level or more.
When the anodes are purged by opening the purge valve, the anodes discharge hydrogen with impurities, and a purge gas flows into a humidifier together with the air discharged from the cathodes.
Then, the vapor in the impurities is used as a source for humidifying a reaction gas needed for an electrochemical reaction of the fuel cells, and the gas including hydrogen and nitrogen is discharged with air to the atmosphere through an exhaust system.
Accordingly, according to this hydrogen purge type, the hydrogen discharged from anodes is mixed with the air discharged from the cathodes and then discharged to the atmosphere through an exhaust system, thereby achieving an effect of reducing the concentration of purge hydrogen by diluting the hydrogen with air.
Further, when a fuel cell system is started or stopped or when a fuel cell vehicle equipped with a fuel cell system is in an idling condition (for example, a fuel cell vehicle is in an ISG condition), a large amount of hydrogen crossing over from the anodes to the cathodes of the fuel cells through a membrane is discharged.
The hydrogen is discharged with air to a humidifier from the cathodes of the fuel cells and is diluted with air through the humidifier, so the hydrogen is discharged to the atmosphere through an exhaust system with the concentration reduced.
However, as described above, although in the related art the concentration of hydrogen to be discharged is slightly reduced by mixing the hydrogen with air discharged from cathodes in a humidifier in accordance with the operation conditions of fuel cell systems, it is difficult to sufficiently mix the hydrogen and air, so the concentration of the hydrogen is not remarkably decreased.
Accordingly, in the related art, since the concentration of hydrogen discharged from fuel cell systems is not effectively reduced and there is quite a possibility of discharging hydrogen that has not been diluted, depending on the operation conditions of the fuel cell systems, the discharged hydrogen having concentration over a predetermined level may cause ignition and explosion.
In order to prevent this problem, measures to discharge hydrogen after reducing the concentration of the hydrogen to be discharged through an exhaust system to a predetermined level or less should be necessarily applied to fuel cell systems.
Recently, in order to prevent the possibility of ignition and explosion by hydrogen discharged from fuel cells, the concentration of hydrogen that fuel cell systems discharge to the atmosphere through exhaust systems is regulated less than 8% at the maximum and less than 4% per three seconds on the average by governmental regulations and relevant laws.
The Description of the Related Art is made to help understanding the background of the present invention and may include matters out of the related art known to those skilled in the art.